Pneumatically powered linear actuator control apparatus and method

Abstract

A combination drive and method for applying power through a piston rod (A) operated by an air cylinder (B) is controlled by an elongated self-locking threaded drive member (C) rotated by an electric motor (D) for affording positioning and velocity control for the air operated cylinder and the guided piston rod which stops and is positively positioned upon cessation of operation of the electric motor. Control apparatus includes a valve housing (35) positioning a spool (40) fixed on one end to the elongated threaded drive member (C), and an assembly (45) for moving the spool axially in respect to the electric motor (D) through an axially compliant coupling (50) so that by controlling the motor the valve is thereby controlled.

What is claimed is: 
     
       1. Control apparatus for a linear actuator having an extensible member, an air operated apparatus including a cylinder extending and retracting a piston for moving an external load, and an elongated threaded lead screw carried in alignment in said cylinder and driven by an electric motor for positioning the load comprising: a valve housing positioned between said electric motor and said cylinder for selectively distributing air under pressure to an extend side of said cylinder and to a retract side of said cylinder;   a valve spool in said valve housing connectable on one end to and in alignment with said elongated threaded lead screw and on the other end to and in alignment with said electric motor for controlling said selectively distributing air;   an assembly for moving said valve spool toward said electric motor responsive to rotation of said elongated threaded member in one direction and toward said cylinder responsive to rotation of said elongated threaded member in the other direction and   a coupling connecting the other end of said valve spool to the electric motor permitting said moving of said valve spool and driving said elongated threaded lead screw for said rotation.   
     
     
       2. The control apparatus set forth in claim 1 wherein said spool is fixedly connected to an adjacent end of said lead screw. 
     
     
       3. The control apparatus set forth in claim 1 wherein said spool is connected to an output shaft of said electric motor through an axially compressible coupling having sufficient rigidity to transmit torque from said electric motor to rotate said lead screw. 
     
     
       4. The control apparatus set forth in claim 3 wherein said coupling is a compressible bellows in axial alignment with said output shaft and said spool. 
     
     
       5. The control apparatus set forth in claim 1 wherein said assembly includes a nut fixed in respect to said piston engaging the threads of said lead screw; and means fixing said piston against rotary motion. 
     
     
       6. The control apparatus set forth in claim 1 wherein said spool includes integral longitudinally spaced annular sealing members arranged to be moved to selected sealing positions distributing air under pressure from said valve. 
     
     
       7. Control apparatus for a linear actuator having an extensible member, an air operated apparatus including a cylinder extending a piston carrying the extensible member for moving an external load, and an elongated threaded lead screw carried in alignment in said cylinder and driven by an electric motor for positioning the load comprising; a valve positioned between said electric motor and said cylinder for selectively distributing air under pressure to an extend side of said cylinder;   a valve spool in said valve connectable on one end to and in alignment with said elongated threaded lead screw and on the other end to an in alignment with said electric motor for controlling said selectively distributing air;   an assembly for moving said valve spool toward said electric motor responsive to rotation of said elongated threaded member in one direction; and   a coupling connecting the other end of said valve spool to the electric motor permitting said moving of said valve spool and driving said elongated threaded lead screw for said rotation.   
     
     
       8. The control apparatus set forth in claim 7 wherein said coupling is axially compressible and in axial alignment with said electric motor. 
     
     
       9. A method of controlling a linear actuator having an extensible member, an air operated apparatus including a cylinder extending and retracting a piston for moving an external load, and an elongated threaded member carried in alignment in said cylinder and driven by an electric motor for positioning the load comprising: positioning a valve between said electric motor and said cylinder;   selectively distributing air under pressure to an extended side of said cylinder and to a retract side of said cylinder through said valve;   connecting a valve spool in said valve on one end to and in axial alignment with said elongated threaded member and on the other end to and in alignment with said electric motor controlling said selectively distributing air to said cylinder;   moving said valve spool in respect to said electric motor responsive to rotation of said elongated threaded member, and   connecting the other end of said valve spool to the electric motor permitting said moving of said valve spool and driving said elongated threaded member for said rotation.   
     
     
       10. The method set forth in claim 9 including the steps of providing a fixed connection between said spool and said elongated threaded member on one end; and providing an axially compliant connection to the other end capable of delivering torque from the motor to the threaded members. 
     
     
       11. The method set forth in claim 10 including the step of providing a nut fixed with respect to said piston on engagement with threads of said threaded member; and securing said piston against rotation.